TWI409170B - Anti - reflective multilayer laminated film - Google Patents

Abstract

A laminated film obtained by carrying out anti-reflection processing on the surface of a reflection polarizing film. This laminated film comprising (A) a monoaxially oriented laminated film consisting of 501 or more alternating first layers made of a first thermoplastic resin having a positive stress optical coefficient and a thickness of 0.05 to 0.5 μm and second layers made of a second thermoplastic resin different from the first thermoplastic resin and having a thickness of 0.05 to 0.5 μm, and a low-reflectance layer formed on at least one side of the monoaxially oriented laminated film and having a reflectance of the surface measured from the input side of 3% or less.

Description

Anti-reflection multilayer laminated film

The present invention relates to a configuration in which a low liquid crystal display layer and a high refractive index layer are alternately arranged, and the refractive index thereof is controlled by stretching so that the interlayer refractive index difference and the thickness of each layer of a specific polarizing component are selectively arbitrary. a uniaxially stretched laminated film with light reflection in a wavelength band, an antireflection film provided on one or both sides thereof, a uniaxially stretched multilayer laminated film for use in a reflective polarizing plate, and a brightness enhancement for liquid crystal display The film.

The multilayer laminated film is obtained by alternately laminating a low refractive index layer and a high refractive index layer, and by optical interference of the structure between the layers, an optical interference film for selectively reflecting or penetrating light of a specific wavelength can be obtained. Further, in such a multilayer laminated film, the film thickness is gradually changed, and a film having a different reflection peak is adhered, and the same high reflectance as that of the metal film can be obtained, and a metallic gloss film and a mirror can be used. Further, such a multilayer laminated film may be stretched in only one direction, and a polarizing reflective film which reflects only a specific polarizing component may be used; and it may be used as a liquid crystal display or the like as a brightness enhancement film for liquid crystal display or the like. .

In general, in a multilayer optical film comprising a layer having a different refractive index of a layer thickness of 0.05 to 0.5 μm, the refractive index difference and the film thickness and the number of laminations of the layer constituting the other layer are formed by the layer constituting the other layer. A so-called anti-reflection phenomenon that reflects light of a specific wavelength can be found. Generally, the reflection wavelength thereof is expressed by the following formula (1).

λ=2x((n1)x(d1)+(n2)x(d2)) (1) where λ is the reflection wavelength (nm), and n1 and n2 are the refractive indices of the respective layers, d1 D2 is the thickness (nm) of the respective layers.

As disclosed in Japanese Laid-Open Patent Publication No. Hei 04-268505, a resin having a positive stress optical coefficient is used for one layer, and only a specific polarizing component having anisotropy in birefringence can be reflected by uniaxial stretching. Using this principle, it is possible to design, for example, a reflective polarizing film that reflects P-polarized light and allows S-polarized light to penetrate. The birefringence suitable at this time is represented by the following formula (2).

N1x>n2x, n1y=n2y (2) In the formula, n1x and n2x are the refractive indices of the respective layers in the stretching direction, and n1y and n2y are the refractive indices of the respective layers perpendicular to the stretching direction.

JP-A-H09-506837 and WO-01/47711 disclose the use of a polyethylene having a high refractive index layer of polyethylene-2,6-naphthalenedicarboxylate (hereinafter also referred to as PEN) and a low refractive index layer. The biaxially stretched film of the elastomer and the high refractive index layer are exemplified by the use of PEN and the low refractive index layer using a uniaxially stretched multilayer laminated film of PEN copolymerized with 30 mol% of isophthalic acid. The film of one of these films is a resin having a positive stress optical coefficient, and the other layer is a resin having a very small stress optical coefficient; that is, a resin which exhibits a birefringence by stretching to exhibit only a specific polarized light is reflected. Reflective polarizing film. Such a reflective polarizing film can be used as a brightness enhancement film for liquid crystal display.

In general, when the reflective polarizing film of the uniaxially stretched multilayer laminated film is used as a brightness-enhancing film for liquid crystal display, the polarizing component parallel to the plane is included in both directions including the stretching direction and the direction perpendicular to the film surface. The visible light reflectance of polarized light is closer to 100%, and the S-polarized light of the polarizing component perpendicular to the same plane is closer to 0%, which is more suitable. However, in the past, the polarizing film has been reflected, and the P-polarized light of the above plane can achieve a reflectance of 90% or more, but has a reflectance of about 10 to 15% for the S-polarized light, thereby causing a reflection loss in the liquid crystal display. , resulting in reduced brightness.

As described above, the reflected light-transmitting film of the uniaxially stretched multilayer laminated film is used, and the light reflectance of the visible light which is polarized to the plane S which is the direction of the stretching direction and the vertical direction is about 10 to 15%. This is mainly due to the interface reflection due to the difference in refractive index between the film substrate and the air interface. The method of reducing the reflection of such an interface is anti-reflection processing.

In general, anti-reflective coating used for displays and the like, coating of only one layer does not reduce the reflectance throughout the entire visible light region, and two layers of the substrate/high refractive index layer/low refractive index layer can be used, or the base layer can be used. Three-layer coating of a medium refractive index layer/high refractive index layer/low refractive index layer or the like.

The method for forming the antireflection film described above is a wet coating method in which a solution is applied to a film, followed by drying, lamination, and a dry method by sputtering, vapor deposition, etc.; the former is difficult to accurately coat the film. The thickness is reproduced and laminated, and the latter method uses a high-precision vacuum, so that the production cost is increased and the productivity is low, and there are manufacturing problems.

For the above reasons, there has been no anti-reflection processing suitable for use on the surface of a reflective polarizing film.

[Disclosure of the Invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems of the conventional multilayer laminated film, and to provide a uniaxially stretched multilayer laminated film which can be used for a reflective polarizing plate in order to increase the brightness effect.

Another object of the present invention is to provide a brightness-enhancing film for liquid crystal display formed by the above uniaxially stretched multilayer film of the present invention.

Still another object of the present invention is to provide a method for producing a uniaxially stretched laminated film constituting the above uniaxially stretched multilayer film of the present invention.

Other objects and advantages of the invention will be apparent from the description which follows.

According to the present invention, the above objects and advantages of the present invention are as follows: (1) a first layer formed of a first thermoplastic resin having a positive stress optical coefficient and having a thickness of 0.05 to 0.5 μm, and a first layer a second layer of a thermoplastic resin different from the second thermoplastic resin and having a thickness of 0.05 to 0.5 μm, a uniaxially stretched laminated film in which 501 or more layers are alternately added, and a uniaxially stretched laminated film a low reflectance layer having a reflectance of 3% or less on the incident side of at least one surface; (B) a direction in which the uniaxially stretched laminated film is stretched and a direction perpendicular to the film surface In the two directions, the average reflectance of the parallel polarizing components is 90% or more in the wavelength range of 400 to 800 nm, and the vertical polarizing component is applied to the surface of the film containing the stretching direction and the direction perpendicular to the film surface. The average reflectance is 10% or less in the range of wavelength 400 to 800 nm; then, (C) is suitably used for a reflective polarizing plate; and it is characterized in that a multilayer laminated film is uniaxially stretched.

According to the present invention, it is a second object of the present invention to provide a brightness-enhancing film for liquid crystal display comprising the uniaxially stretched multilayer film of the present invention.

According to the present invention, the above object and advantage of the present invention is that the third layer (A) is made of a first thermoplastic resin having a positive stress optical coefficient and has a thickness of 0.05 to 0.5 μm, and is first and a second layer of a thermoplastic resin different from the second thermoplastic resin and having a thickness of 0.05 to 0.5 μm, a uniaxially stretched laminated film in which 501 or more layers are alternately added, and a uniaxially stretched laminated film a low refractive index layer having a refractive index of at least 1.1 to 1.45 on one side; (B) a polarizing component parallel to a direction including a stretching direction of the uniaxially stretched laminated film and a direction perpendicular to a direction of the film surface The average reflectance is 90% or more in the range of wavelength 400 to 800 nm, and the average reflectance of the vertical polarizing component is 400 to 800 nm in the direction of the film extending direction and the direction perpendicular to the film surface. The range is 10% or less; then, (C) is suitable for use in a polarizing plate; characteristically, it is achieved by uniaxially stretching a multilayer laminated film.

Further, according to the present invention, the above objects and advantages of the present invention are the fourth thermoplastic resin having a melting point of 260 to 270 ° C and a second thermoplastic resin having a melting point lower than the melting point of the first thermoplastic resin by 15 to 60 ° C. a first step of alternately laminating 501 layers or more to form a sheet; a second step of stretching the obtained sheet in either of a pulling direction or a width direction by 2 to 10 times; and subjecting the obtained stretched sheet to a second thermoplastic resin The third step of heat treatment at a temperature at which the melting point is 10 ° C lower than the temperature of the first thermoplastic resin by 15 ° C is characterized by the uniaxially stretched multilayer laminated film manufacturing method. Achieved.

[The best form for implementing the invention]

The invention is described in detail below.

<uniaxially stretched laminated film>

In the present invention, the resin constituting the first layer is necessarily a first thermoplastic resin having positive stress birefringence (synonymous with stress optical coefficient). The first thermoplastic resin having positive stress birefringence is, for example, polyethylene-2,6-form dicarboxylate (hereinafter referred to as 2,6-PEN) and its isomers (for example, 1,4-, 1,5-, 2,7- and 2,3-PEN), polyalkylene terephthalates (eg polyethylene terephthalate, polybutylene terephthalate, and polypairs) 1,4-cyclohexanedimethylene phthalate) polyisophthalic acid ethylene glycol, polyimide (for example, polyacrylamide), polyether quinone, polyalkene polymer (eg polyethylene, polypropylene, polybutene, polyisobutylene and poly(4-methyl)pentene), fluorinated polymers (eg perfluoroalkoxy resins, polytetrafluoroethylene, fluorinated ethylene-propylene copolymerization) , polyvinylidene fluoride and polychlorotrifluoroethylene), chlorinated polymers (such as polyvinylidene chloride and polyvinyl chloride), polyfluorene, polyether oxime, polyacrylonitrile, polyamine, oxime, ring Oxygen resins, polyvinyl acetate, polyether amides, ionomers, elastomers (e.g., polybutadiene, polyisoprene, and chloroprene rubber), and polyurethanes and the like.

Among them, polyethylene 2,6-naphthalene dicarboxylate (2,6-PEN) having a large stress birefringence and its isomers (for example, 1,4-, 1,5-, 2,7- And 2,3-PEN), polyalkylene terephthalate (such as polyethylene terephthalate, polybutylene terephthalate, and polybutylene terephthalate 1,4-cyclohexane Alkyl dimethylene ester) is suitable. In particular, 2,6-, 1,4-, 1,5-, 2,7-, and 2,3-PEN are more suitable.

Further, the above-mentioned polyethylene 2,6-naphthalenedicarboxylic acid ethylene glycol refers to ethylene-2,6-naphthalenedicarboxylate as a main repeating unit, for example, ethylene glycol 2,6-naphthalenedicarboxylate. The ester is 80-100 mol% of the total repeat unit, and is more suitable for 90-100 mol%, including the homopolymer and the copolymer; the other isomers are also the same. Similarly, polyethylene terephthalate refers to ethylene terephthalate as the main repeating unit, for example, ethylene terephthalate is 80 to 100 moles of the repeating unit. %, more preferably 90 to 100 mol%, including homopolymers and copolymers.

The second thermoplastic resin constituting the second layer, other than the above-exemplified thermoplastic resin as the first thermoplastic resin, such as random polystyrene, polycarbonate, polymethacrylate (for example, polymethacrylate) Ester, polypropyl methacrylate, polyethyl methacrylate, polymethyl methacrylate), polyacrylate (such as polybutyl acrylate and polymethyl acrylate), syndiotactic polystyrene (sPS), Syndiotactic main poly-α-methylstyrene, syndiotactic polydichlorostyrene, copolymers and blends of such random polystyrene, cellulose derivatives (such as ethylcellulose) , cellulose acetate, cellulose propionate, cellulose acetate butyrate, and nitrocellulose) and the like.

The second thermoplastic resin must be different from the first thermoplastic resin, but does not necessarily have to have positive stress birefringence (synonymous with the stress optical coefficient). However, when a second thermoplastic resin having a positive stress birefringence is used, it is preferably 15 to 60 ° C lower than the melting point of the first thermoplastic resin; wherein, from the viewpoint of interlayer adhesion, the use is lower than the first A particularly suitable copolymer of 2,6-, 1,4-, 1,5-, 2,7- or 2,3-PEN having a melting point of 15 to 60 ° C is more suitable. Such copolymers are copolymers of PEN, such as 2,6-, 1,4-, 1,5-, 2,7-, and/or 2,3-naphthalenedicarboxylic acid or esters thereof, (a) Terephthalic acid or its ester, (b) isophthalic acid or its ester, (c) phthalic acid or its ester, (d) alkanediol, (e) cycloalkanediol, such as cyclohexanedicarboxylic acid , (f) alkanedicarboxylic acid and / or (g) a cycloalkanedicarboxylic acid, such as a copolymer of cyclohexanedicarboxylic acid; a copolymer of a polyalkylene terephthalate, such as terephthalic acid or And (a) naphthalene dicarboxylic acid or its ester, (b) isophthalic acid or its ester, (c) phthalic acid or its ester, (d) alkanediol, (e) cycloalkanediol, For example, cyclohexanedicarboxylic acid, (f) alkanedicarboxylic acid and/or (g) a cycloalkanedicarboxylic acid such as a copolymer of cyclohexanedicarboxylic acid; a styrene copolymer such as styrene-butadiene copolymer And a styrene-acrylonitrile copolymer; and a copolymer of 4,4'-dibenzoic acid and ethylene glycol, and the like.

A suitable example of the uniaxially stretched laminated film of the present invention will be described in more detail below.

In a most suitable embodiment of the present invention, the first thermoplastic resin constituting the first layer is a polyester obtained by using a 2,6-naphthalenedicarboxylate component as a main repeating unit. It is suitable that the homopolymerized ethylene 2,6-naphthalenedicarboxylate or the 95 mol% of the repeating unit can be maintained at a higher melting point than the polyester constituting the second layer described later as 2,6-naphthalene The ethylene glycol dicarboxylate component is copolymerized with ethylene glycol 2,6-naphthalene dicarboxylate. When the molar amount of the ethylene compound of 2,6-naphthalenedicarboxylate is less than 95% by mole of the repeating unit, the melting point is lowered, and the difference in melting point from the polyester constituting the second layer described later cannot be obtained, and as a result, it cannot be imparted. The stretched laminate film has a sufficient refractive index difference. Among them, homopolymerized 2,6-naphthalenedicarboxylate which can maintain a high melting point is suitable. a copolymerization component other than the ethylene glycol 2,6-naphthalene dicarboxylate component, and other aromatic carboxylic acids such as isophthalic acid and 2,7-naphthalenedicarboxylic acid; adipic acid and sebacic acid; An aliphatic dicarboxylic acid such as azelaic acid or a decane dicarboxylic acid; an acid component such as an alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid; an aliphatic diol such as butanediol or hexanediol; A diol component such as an alicyclic diol such as hexane dimethanol.

However, the melting point of the resin constituting the first layer is in the range of 260 to 270 ° C, and it is preferable to increase the difference in melting point of the resin constituting the second layer to be described later. When the melting point of the resin constituting the first layer is less than the lower limit, the difference in melting point from the resin constituting the second layer is small, and as a result, it is difficult to impart a sufficient refractive index difference to the obtained uniaxially stretched film. Further, the homopolymerized ethylene glycol 2,6-naphthalenedicarboxylate has a melting point of about 267 °C.

In a most suitable embodiment of the present invention, the second thermoplastic resin constituting the second layer is a polyester composed of a main repeating unit of ethylene glycol 2,6-naphthalene dicarboxylate having a melting point of 210 to 255 °C. . In particular, from the viewpoint of film formability in uniaxial stretching, a crystalline polyester is suitable. Further, it is possible to make the melting point 40 to 98.5 mol% lower than the repeating unit constituting the first layer of the polyester, and more preferably 75 to 97 mol%, which is 2,6-naphthalenedicarboxylic acid ethylene Alcohol ester component; 1.5~60 mol%, more suitable for 3~25 mol%, other than copolymerization components such as ethylene terephthalate and / or isophthalic acid B A total of 2,6-naphthalenedicarboxylate ethylene glycol ester. When the molar amount of the ethylene glycol of 2,6-naphthalenedicarboxylate is less than 75 mol% of the repeating unit and the molar number of the copolymerized component exceeds 25 mol%, the polymer is substantially amorphous. The film forming property of the uniaxial stretching is lowered, and the composition of the polyester constituting the first layer described above is greatly different, and the adhesion between the layers is liable to lower. On the other hand, when the molar amount of the ethylene glycol of 2,6-naphthalenedicarboxylate exceeds 97 mol% of the repeating unit and the molar number of the copolymerized component is less than 3 mol%, The difference in melting point of the polyester of the first layer is reduced, and as a result, it is difficult to impart sufficient reflectance to the stretched laminated film. a copolymerization component other than the ethylene glycol 2,6-naphthalene dicarboxylate component, and other aromatic carboxylic acids such as isophthalic acid and 2,7-naphthalene dicarboxylic acid; adipic acid and sebacic acid; An aliphatic dicarboxylic acid such as azelaic acid or a decane dicarboxylic acid; an acid component such as an alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid; an aliphatic diol such as butanediol or hexanediol; A diol component such as an alicyclic diol such as hexane dimethanol. Among them, terephthalic acid or isophthalic acid is preferred, in particular, from the viewpoint of maintaining the stretchability in comparison and easily lowering the melting point.

However, the melting point of the second thermoplastic resin constituting the second layer is in the range of 210 to 255 ° C, and it is preferable to increase the difference in melting point from the first thermoplastic resin constituting the first layer. When the melting point of the second thermoplastic resin constituting the second layer is higher than the upper limit, the difference in melting point from the first thermoplastic resin constituting the first layer is decreased, and as a result, it is difficult to impart a sufficient refractive index difference to the obtained stretched laminated film. On the other hand, when the melting point of the second thermoplastic resin constituting the second layer is less than the lower limit, the composition of the first thermoplastic resin constituting the first layer is largely changed, and it is difficult to impart sufficient interlayer between the obtained uniaxially stretched laminated films. Adhesiveness. Further, the melting point of the second thermoplastic resin constituting the second layer is not necessarily lowered from the stage before the film formation, and may be lowered after the stretching treatment. For example, it is preferable to prepare a homopoly 2,6-naphthalenedicarboxylate and other polyesters, and to melt and knead them, and it is also possible to carry out transesterification.

The first layer and the second layer selectively reflect light by light interference between the layers, and the thickness of each of the first layer and the second layer is in the range of 0.05 to 0.5 μm. The reflection characteristics of the multilayer optical film are determined by the number of layers, the difference in refractive index, and the thickness of the layer. In the present invention, the reflection wavelength band shown by the uniaxially stretched laminated film is required to be in the range of the above layer thickness from the visible light region to the near-infrared region. When the layer thickness exceeds 0.5 μm, the reflection band becomes an infrared region, and a suitable reflective polarizing film cannot be obtained. On the other hand, when it is less than 0.05 μm, the reflection band of the light-emitting light becomes an ultraviolet region, and substantial energy cannot be obtained.

In the uniaxially stretched laminated film of the present invention, the number of laminations is required to be at least 501 layers. When the number of layers is less than 501 layers, the optical characteristics for the above purpose cannot be satisfied in the range of wavelengths of 400 to 800 nm. The upper limit of the number of lamellas is the most suitable for the 2001 layer from the viewpoints of productivity and film rationality.

In the uniaxially stretched laminated film, the ratio of the average thickness of the first layer to the average thickness of the second layer is preferably 0.5 to 5.0, more preferably 1.0 to 4.0, and most preferably 1.5 to 3.5. The adhesion between the layers can be maintained by changing the thickness ratio of the first layer to the second layer; further, the mechanical properties of the uniaxially stretched laminated film can be adjusted without changing the resin used. When the ratio of the average thickness of the first layer to the average thickness of the second layer is less than 0.5, the tensile direction of the uniaxially stretched laminated film is easily torn; on the other hand, when it exceeds 5.0, the difference between the treatment and the directional relaxation is single. The change in the thickness of the axially stretched laminated film is apt to increase.

Further, in the optical multilayer film, the wavelength of reflection is determined by the refractive index, the number of layers, and the thickness of the layer according to the above formula (1). When the first layer and the second layer which are laminated are each a certain thickness, only the reflection can be performed. Specific wavelength.

In the uniaxially stretched laminated film of the present invention, the ratio of the maximum thickness to the minimum thickness of the first layer and the second layer is preferably 1.5 to 5.0, more preferably 2.0 to 4.0, and most preferably 2.5 to 3.5. The first layer and the second layer may be changed in stages, and continuous changes may also be made. With the respective changes of the first layer and the second layer thus laminated, light of a wider wavelength region can be reflected. When the ratio of the maximum thickness to the minimum thickness of the first layer and the second layer is less than 1.5, it is difficult to cover the range of the wavelength region of 400 to 800 nm as the reflection characteristic for the above purpose. On the other hand, when it exceeds 5.0, the reflectance band is too broad and the reflectance is lowered, and it is difficult to obtain the reflection characteristics of the above object. Further, in this case, the laminated structure may be a surface layer of a multilayer structure in which the stepwise or continuous change is performed, or a layer of 0.5 μm or more or more may be present inside.

In the uniaxially stretched laminated film of the present invention, the average reflectance of the polarizing component parallel to the plane containing the uniaxially stretched film and the direction perpendicular to the direction of the film surface is at a wavelength of 400 to 800. The range is more than 90%, more suitable for 95% or more, and more preferably 98% or more; the average reflectance of the polarizing component perpendicular to the same plane is 10% or less in the range of wavelength 400 to 800, and is preferably 5% or less. It is preferably 3% or less, and most preferably 1% or less. For the plane containing the uniaxially stretched film and the direction perpendicular to the direction of the film surface, the average reflectance of the parallel polarized components is less than 90% in the wavelength range of 400 to 800 nm, and is used as the reflective polarized light. The polarized reflection performance of the film is insufficient, and the enhanced brightness film such as a liquid crystal display cannot exhibit sufficient performance. Further, when the average reflectance of the polarizing component perpendicular to the same plane exceeds 10%, the polarized light transmittance of the reflective polarizing film is lowered in the range of 400 to 800 nm, and it is used as a brightness enhancement film for liquid crystal display or the like. The performance is degraded.

In the uniaxially stretched laminated film, the parallel polarized component is in the range of 400 to 800 nm in the plane of the uniaxially stretched film and the plane perpendicular to the direction of the film surface, and the maximum reflectance is obtained. The difference between the minimum reflectance and the minimum reflectance is 10%, and the polarization component perpendicular to the same plane is in the range of 400 to 800 nm, and the difference between the maximum reflectance and the minimum reflectance is preferably within 10%. When the difference between the maximum reflectance and the minimum reflectance of the polarizing component exceeds 10%, any one of the light hue of reflection or penetration is generated, which may cause problems in liquid crystal display or the like.

Fig. 1 is a view showing an example of a reflectance curve of a uniaxially stretched laminated film of the present invention. P-polarized light is a parallel polarizing component in a plane containing both the stretching direction of the film and the direction perpendicular to the film surface, and the S-polarized light is a plane in both directions of stretching of the film and directions perpendicular to the film surface. Vertical polarizing component.

In the uniaxially stretched laminated film of the present invention, the method of laminating the multilayer structure is not particularly limited, and for example, the polyester as the first layer is branched into 251 layers, and the polyester layer as the second layer is used. Divided into 250 layers, and then alternately laminating the first layer and the second layer, using a method of continuously changing the flow path by 1 to 3 times the multi-layer feeding unit device; by means of a multi-layer feeding unit device, 201 layers The uniform layer is laminated, and the laminated fluid is further laminated to 601 layers perpendicular to the lamination surface at a ratio of 1.0:1.3:2.0. It is also possible to use these two in combination.

In the uniaxially stretched laminated film of the present invention, at least 501 layers of the first layer and the second layer are alternately laminated. Further, as described above, the uniaxially stretched laminated film of the present invention is stretched in the uniaxial direction for the purpose of satisfying the optical characteristics of the reflective polarizing film. In this case, the stretching direction is the longitudinal direction and the stretching may be performed in the transverse direction. Moreover, it is also possible to provide a plurality of stages of stretching in a range in which optical characteristics are satisfied. Further, as the stretching method, a well-known stretching method such as heating by a rod heater, drum heating stretching, tenter stretching, or the like can be used, from the viewpoint of reducing defects and stretching speed by contact with the roller. In other words, it is more suitable to stretch with a tenter. Further, the term "uniaxial stretching" does not mean that the film is not stretched completely in the direction perpendicular to the uniaxial stretching direction, and is included in the direction perpendicular to the direction of, for example, 1.2 times or less, and more preferably 1.1 times or less.

In particular, from the viewpoint of ensuring the adhesion between the layers and the film forming property of the stretching process, the first layer and the second layer of the uniaxially stretched laminated film of the present invention are simultaneously composed of a crystalline resin exhibiting a positive stress optical coefficient. After the second thermoplastic resin of the second layer is stretched, at least a portion of the melt-relaxed orientation is extremely suitable. It is determined by DSC (differential scanning calorimeter) that the uniaxially stretched laminated film thus obtained has two or more melting points, and such a melting point has a difference of 5 ° C or more, which is suitable. Here, the first thermoplastic resin having a higher melting point is the first layer exhibiting a high refractive index, and the lower melting point is a second thermoplastic resin exhibiting a second layer having a low reflectance. Further, since at least a part of the second layer after the stretching is melted, the crystallization peak measured by DSC exists in the range of 150 to 220 ° C, which is very suitable. When the crystallization peak is 150° C. or lower, the film is strongly crystallized when the film is stretched, and the film formability at the time of film formation is lowered, and the uniformity of the film quality is likely to be lowered. As a result, a hue of the hue or the like may occur. On the other hand, when the crystallization peak is 220° C. or more, in the production method described later, the second layer is melted by the heat setting treatment to cause crystallization, and it is difficult to develop a sufficient refractive index difference.

As described above, the uniaxially stretched laminated film of the present invention can obtain a uniform film of the film by stretching the first thermoplastic resin which simultaneously exhibits the first layer of crystallinity and the second thermoplastic resin of the second layer; And melting the second layer after the stretching step can improve interlayer adhesion while improving reflection performance. Therefore, in the uniaxially stretched laminated film of the present invention, uniaxially stretched lamination of two or more melting peaks having crystal melting peaks present at 150 to 220 ° C and melting point difference of 5 ° C or more is observed by DSC. The film is extremely suitable. Further, in the uniaxially stretched laminated film of the present invention, the breaking strength in the direction of the stretching treatment is preferably 100 MPa. When the breaking strength is less than 100 MPa, the handleability of the uniaxially stretched laminated film at the time of processing is lowered, and the durability at the time of product formation is lowered. Further, when the breaking strength is 100 MPa or more, the film is tough and has the advantage of improving the take-up property. A suitable breaking strength is 150 MPa or more in the longitudinal direction, more preferably 200 MPa or more, and 150 MPa or more in the transverse direction, and more preferably 200 MPa or more. Further, when the strength ratio in the longitudinal direction and the lateral direction is 3 or less, it is suitable for having sufficient tear resistance. In particular, when the strength ratio in the longitudinal direction to the lateral direction is 2 or less, the tear resistance is further improved, which is suitable. The upper limit of the breaking strength is not particularly limited, and from the viewpoint of maintaining the stability of the stretching step, it is preferably at most 500 MPa.

Moreover, the uniaxially stretched laminated film of the present invention is characterized in that the first thermoplastic resin is polyethylene-2,6-naphthalenedicarboxylate, and the thermal dimensional stability is very high, especially in the processing process. When the temperature is higher than °C, it can fully correspond. The heat shrinkage ratio at the time of the treatment at 150 ° C for 30 minutes in the stretching treatment direction (any one of the film forming direction and the width direction) of the film is preferably 5.0% or less, more preferably 1.5% or less, and most preferably 1.0% or less. Further, in the uniaxially stretched laminated film of the present invention, the heat shrinkage ratio in any one of the film forming direction and the width direction at the time of treatment at 200 ° C for 10 minutes is preferably 3.0% or less, more preferably 20% or less, and 1.5% or less. The following is ideal.

Further, in the uniaxially stretched laminated film of the present invention, the resin constituting the first layer and the second layer is preferably a crystalline resin as described above. When the resin constituting the first layer and the second layer is a crystalline resin at the same time, the treatment such as stretching does not cause unevenness, and as a result, the thick spot of the film can be reduced. The thickness variation range is preferably 10% or less as shown by the following formula (3), more preferably 5% or less, and most preferably 3.0% or less. When the variation rate of the film thickness is 10% or more, any of the optical characteristics is increased, and optical characteristics for the purpose of discoloration of the hue are not obtained.

Thickness variation rate (%) = (T _{m a x -} T _{m i n} ) / (T _{A v e} ) (3) T _{m a x} in the above formula is the maximum thickness, and T _{m i n} is the minimum thickness And T _{A v e} is the average thickness.

The uniaxially stretched laminated film of the present invention is suitable for improving the take-up property of the film, and is preferably 0.001 to 0.5% by weight based on the weight of the uniaxially stretched laminated film on one of the first layer or the second layer. More preferably 0.005 to 0.2% by weight of inert particles are preferred. The average particle diameter of the inert fine particles is preferably 0.01 to 2 μm, more preferably 0.05 to 1 μm, and most preferably 0.1 to 0.3 μm. When the average particle diameter is less than the lower limit and the content is also small, the lower limit is easy, and the effect of improving the take-up property of the uniaxially stretched laminated film is insufficient. On the other hand, when the content of the inert fine particles exceeds the upper limit and the average particle diameter exceeds the upper limit, The microparticles cause a significant deterioration in the optical properties of the multilayer stretched film, which is extremely unsuitable.

<Method for Producing Uniaxially Stretched Laminate Film>

The most suitable examples are detailed below.

The uniaxially stretched laminated film of the present invention is a first thermoplastic resin having a melting point of 260 to 270 ° C, for example, a polyester having a main repeating unit of ethylene 2,6-naphthalenedicarboxylate (No. a second thermoplastic resin having a melting point at least 10 ° C lower than the first thermoplastic resin after the stretching treatment, for example, a 2,6-naphthalenedicarboxylate component as a main repeating unit The polyester (for the second layer) is alternately extruded in a molten state by at least 501 layers or more to form a multilayer unstretched film in a superposed state (step of forming a sheet). At this time, a laminate of 501 or more layers is laminated, and the layer thickness thereof is changed in a stepwise or continuous manner in the range of 1.5 times to 5.0 times to be laminated. Further, the polyesters of the first thermoplastic resin and the second thermoplastic resin are the same as those described for the first layer and the second layer described above. When the melting point of the polyester of the first thermoplastic resin is less than 260 ° C, a sufficient difference in melting point from the polyester of the second thermoplastic resin cannot be obtained, and as a result, it is difficult to provide a sufficient refractive index difference between the layers of the obtained uniaxially stretched laminated film. On the other hand, since the melting point of the homopoly 2,6-naphthalenedicarboxylate is about 267 ° C, the upper limit of the melting point of the first polyester for the first layer is at most 270 ° C. Further, the melting point of the second polyester for the second layer is not more than 15 ° C lower than the first polyester, and a sufficient difference in melting point from the second polyester is not obtained, and as a result, the interlayer of the obtained uniaxially stretched laminated film cannot be imparted. A sufficient refractive index difference. The upper limit of the difference between the melting point of the first polyester and the melting point of the second polyester is preferably from 50 to C from the viewpoint of maintaining the adhesion between the two.

The thus obtained unstretched laminated film is stretched in the uniaxial direction (in the direction of the film surface) in either the film forming direction or the width direction orthogonal thereto. The stretching temperature is preferably in the range of the glass transition point temperature (Tg) to (Tg + 50 ° C) of the first thermoplastic resin such as polyester. At this time, the area magnification is preferably 2 to 10 times. The larger the stretching ratio, the deviation of the surface direction of each of the first layer and the second layer is reduced by stretching thin layering, that is, the light of the uniaxially stretched laminated film is disturbed to be uniform in the plane direction. Therefore, it is very suitable. The stretching method at this time may employ a well-known stretching method such as heating stretching by a rod heater, drum heating stretching, tenter stretching, etc., from the reduction of defects by contact with the roller, the stretching speed, and the like. From the point of view, it is more suitable to stretch with a tenter.

The most characteristic feature of this most suitable method is that the thus stretched laminate film is at a temperature at which the second thermoplastic resin is, for example, 10 ° C lower than the melting point of the polyester, and the first thermoplastic resin is, for example, 15 ° C lower than the melting point of the polyester. The heat treatment between the temperatures moderates the orientation of the molecular chains in the second layer to lower the refractive index of the second layer. When the temperature of the heat treatment is lower than the melting point of the second thermoplastic resin by more than 10 ° C, the effect of lowering the orientation of the molecular chain in the second layer to reduce the refractive index is insufficient, and the sufficient refractive index difference of the obtained uniaxially stretched laminated film cannot be imparted. . On the other hand, when the temperature of the heat treatment is not lower than the melting point of the first thermoplastic resin by 10 ° C or more, the orientation of the molecular chain in the first layer is also relaxed to lower the refractive index, and the obtained uniaxially stretched laminate cannot be obtained. The film has a sufficient refractive index difference. Suitable treatment temperature is a temperature lower than 6 ° C lower than the melting point of the second thermoplastic resin, and a temperature lower than 16 ° C lower than the melting point of the first thermoplastic resin; at a temperature lower than 2 ° C of the melting point of the second thermoplastic resin, A temperature between the temperature lower than the temperature of 18 ° C lower than the melting point of the first thermoplastic resin is more suitable. Also, the heat treatment time is preferably 1 to 60 seconds.

Further, by changing the temperature and time of the heat treatment, the refractive index of the second layer can be adjusted without changing the composition of the resin; that is, the composition of the resin is not changed to change the reflection characteristics of the uniaxially stretched laminated film.

<low reflectivity layer>

The uniaxially stretched multilayer laminated film of the present invention has a low reflectance layer having a surface reflectance of 3% or less on light incident on at least one surface of the uniaxially stretched laminated film. When the surface reflectance of the low reflectance layer (hereinafter also the antireflection laminate layer) is more than 3%, the surface reflection resistance of the uniaxially stretched laminated film is insufficient to prevent the surface from being sufficiently enhanced. effect. It is preferably 2% or less, and more preferably 1% or less.

The antireflection layer used in the present invention is not particularly limited as long as it does not impair the above optical characteristics of the uniaxially stretched laminate film. The specific antireflection layer includes (1) an antireflection layer made of a film of MgF ₂ or the like having a thickness of about 0.1 μm, (2) an antireflection layer formed by forming a metal deposition film, and (3) a refractive index of light. a low refractive index layer formed of a low material is disposed on the uniaxially stretched laminated film, and (4) a high refractive index layer having a high refractive index is disposed on the uniaxially stretched laminated film. An antireflection layer having a lower refractive index layer than the refractive index of the high refractive index layer is disposed on the refractive index layer (for example, a portion of the antireflection layer connected to the uniaxially stretched laminated film to have a high refractive index (6) The ultrafine particle layer of the metal oxide is dispersed, (5) the antireflection layer laminated with the layer of the above (4), and (6) the inner side of the high refractive index layer having a high refractive index (adhesive) a display surface side of the display surface) is provided with a medium refractive index layer having a refractive index lower than that of the high refractive index layer, and is outside the high refractive index layer having a high refractive index (adhesion to the display surface) The side on which the display surface is different) is provided with an antireflection layer of a low refractive index layer having a refractive index lower than that of the medium refractive index layer.

Among them, the low refractive index layer of (4) and the antireflection layer of (6) are more suitable from the viewpoint of enabling more effective antireflection. In particular, it is more preferable to form the medium refractive index layer, the high refractive index layer, and the low refractive index layer in the order of the uniaxially stretched laminated film. Further, the low refractive index layer, the medium refractive index layer, and the high refractive index layer are made of SiO _x , the refractive index of the low refractive index layer is greater than 1.4, the refractive index of the high refractive index layer is less than 2.2, and the low refractive index layer is 80. The thickness of ~110nm, the thickness of the high refractive index layer is 30~110nm, the thickness of the medium refractive index layer is 50~100nm, and the optical film thickness D of each layer (D=n.d, n: medium refractive index layer) The refractive index, d: the thickness of the medium refractive index layer) is preferably an antireflection layer having a wavelength of visible light or less.

Further, the low refractive index layer is preferably a refractive index of 1.1 to 1.45, and more preferably a refractive index of 1.1 to 1.4. When the refractive index is less than 1.1, it is difficult to obtain an antireflection effect, and when the refractive index exceeds 1.45, the effect of antireflection is weakened.

The low refractive index layer can be obtained by first applying a coating liquid composed of the following specific composition to at least one side of the uniaxially stretched laminated film.

The coating liquid is composed of (a) inorganic fine particles substantially composed of oxides of at least one element selected from the group consisting of Si, Al, Ti, and Zr, and coated fine particles obtained by coating the surface of the organic polymer. (b) a binder resin, and (c) an organic solvent having a boiling point of 100 ° C or higher.

The above inorganic fine particles are preferably made of an oxide of Si.

These inorganic fine particles are preferably formed by partial hydrolysis of a metal alkoxide or condensation by a hydrolyzate. The alkoxy group at this time means a substance in which the above element is bonded to an alkoxy group (-OR group). In this case, R is a lower alkyl group, and for example, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, an n-butyl group or an isobutyl group is suitable. Such inorganic fine particles are preferably contained in a part containing a hydroxyl group or an alkoxy group. The alkoxy group can enhance the affinity of the inorganic fine particles with the organic polymer or the binder resin for the purpose of modifying the inorganic fine particles described later, and form a chemical bond therebetween. Further, in the organic solvent, there is an effect of improving the dispersibility of the inorganic fine particles. The metal alkoxide has an alkoxy group in accordance with the valence of its central element, and in the present invention, a metal having 3 to 4 alkoxy groups containing an alkoxy group is suitable.

The particle diameter of the inorganic fine particles is preferably in the range of 5 to 200 nm.

The organic polymer coated with the surface of the inorganic fine particles is, for example, an alkyl polymer, a polymer having a urethane bond, a polymer having an ester bond, a polymer having an ether bond, an acrylic polymer or the like. Among them, an acrylic polymer is suitable from the viewpoint of easy adjustment of the refractive index and superior transparency. Further, the organic polymer has at least one polyoxyalkylene group, and the polyoxyalkylene group contains one or more alkoxy groups, and is extremely suitable from the viewpoint of dispersibility and the like. Examples of the alkoxy group are the same as those described above. Further, such an organic polymer preferably contains a fluorine element.

In the present invention, the particle diameter of the coated fine particles is preferably in the range of 5 to 200 nm. When the surface energy of the fine particles is less than 5 μm, it is likely to aggregate in the coating liquid, and when it exceeds 200 nm, the transparency of the obtained coating film is insufficient.

The binder resin (b) is not particularly limited, and is an alkyl polymer, a polymer having a urethane bond, a polymer having an ester bond, a polymer having an ether bond, an acrylic polymer, and the like. Among them, an acrylic polymer is more suitable from the viewpoint of superior transparency. The acrylic polymer is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, and (meth)acrylic acid. a monofunctional acrylate such as isobutyl ester, tert-butyl (meth)acrylate or 3-hydroxyethyl (meth)acrylate; ethylene glycol di(meth)acrylate; propylene glycol di(meth)acrylate; A polymer having a propylene group polymerized such as a difunctional acrylate such as (meth) acrylate or the like. Further, at least one of the terminals has an alkyl group polymerization of an acryl group, an ether polymer or the like, and further a functional group having a reactive chain such as a hydroxyl group, a carboxyl group, an amine group, an epoxy group, a decyl group or an oxazole. Polymers such as phenyl groups are also suitable for use. The polymer having such a propylene group in the present invention is also referred to as a propylene-based polymer. Among these, an acrylic polymer containing a hydroxyl group in one part of the structure is suitable from the viewpoint of the reaction with a curing agent to be described later.

The organic solvent (c) having a boiling point of 100 ° C or more and mixed with water is propylene glycol monomethyl ether (PGM, boiling point 121 ° C), propylene glycol monomethyl ether acetate (PGMA, boiling point 146 ° C), ethylene glycol monobutyl ether (EGB, boiling point 171 ° C), methyl isobutyl ketone (MIBK, boiling point 115 ° C), isobutyl acetate (IBAc, boiling point 127 ° C), methyl n-butanone (MNBK, boiling point 128 ° C) and the like. Among them, methyl isobutyl ketone, isobutyl acetate, and methyl n-butanone are suitable, and methyl isobutyl ketone is most suitable. In a solvent such as toluene or methyl ethyl ketone which does not mix with water at a boiling point of less than 100 ° C, the refractive index of the obtained low refractive index layer hardly changes at all even if the solid content concentration is changed. When the boiling point is 100 ° C or higher, 100 to 150 ° C is more preferable, and the most suitable organic solvent is 100 to 130 ° C, the composition of the solid component constituting the low refractive index is the same, and the composition of the coating liquid is changed by changing the solid content concentration or the like. There is an advantage that the refractive index of the resulting low refractive index layer can be adjusted. When the boiling point of the solvent is lower than the lower limit, the low refractive index of the present invention cannot be achieved; when the upper limit is exceeded, the line speed is slow at the time of production, and it is necessary to increase the temperature of the oven, which is not suitable. Further, the organic solvent may be mixed with water. The term "mixable with water" means having a polar group such as a hydroxyl group or a carbonyl group. For example, the organic solvent is preferably 1% by weight or more, and more preferably 5% by weight. The meaning of the mixed state. It has the advantage of adjusting the refractive index without changing the composition of the solid component constituting the low refractive index, and can correspond to various refractive indices of a single composition. In other words, the low refractive index is not only low in refractive index, but also the refractive index of the base film which can be formed, and the optimum refractive index of each of the amplitude conditions is satisfied. Therefore, even if a plurality of low refractive indexes are not prepared for the plurality of base films. The material of the layer has the advantage of obtaining a layer close to the optimum refractive index in a single composition. When the boiling point of the organic solvent is less than 100 ° C, the solvent is rapidly volatilized during drying after coating, and a uniform void cannot be obtained, so that a change in refractive index is not observed. Moreover, when the coating is dried, the temperature of the coating liquid is lowered by the heat of vaporization, and the water in the air is once entangled in the coating liquid and then volatilized, thereby forming a gradient of the evaporation rate of the solvent and the water so that the drying does not occur. Evenly, a large void is formed in the coating film to lower the transparency of the coating film, and it is necessary to use a high boiling point solvent which can be mixed with water and has a small difference in volatilization rate of the solvent after mixing.

However, as described above, the lower the refractive index of the low refractive index layer, the better the refractive index of the film substrate to be used, and the optimum refractive index satisfying the respective amplitude conditions. For example, when the film substrate is a polyethylene naphthalate film, a refractive index as disclosed in the above-mentioned JP-A-2003-292805, that is, a low refractive index layer having a refractive index of 1.3 or more can be obtained. Antireflection performance; when a film substrate such as polyethylene terephthalate film or triethylenesulfonyl cellulose, a low refractive index layer having a refractive index of 1.3 or more cannot obtain good antireflection performance. However, according to the method of the present invention, a low refractive index layer having a low refractive index of 1.10 to 1.29 is formed on the surface of the film substrate.

The method of obtaining such a particularly low refractive index is, for example, a reduction in the concentration of the solid portion in the coating liquid, an increase in the ratio of the organic solvent which can be mixed with water and having a boiling point of 100 ° C or more, or the selection of the drying after coating is easy. An organic solvent or the like remaining in the coating film. From such a viewpoint, the organic solvent which can be mixed with water and has a boiling point of 100 ° C or more is more preferably 70% by weight or more in the coating liquid, more preferably 80% by weight or more, and even more preferably 90% by weight or more. It is most desirable to use 95% by weight or more. When the amount used is less than this range, it is difficult to form voids in the low refractive index layer during drying, and convection occurs when volatilization of other solvents present in the coating liquid, and the low refractive index layer may be fogged during drying. Further, the solid content concentration of the low refractive index layer formed during the coating is in the range of 0.5 to 10% by weight, and further, the refractive index is easily adjusted in the range of 0.5 to 5 by weight, which is extremely suitable. Further, from the viewpoint of lowering the refractive index, the solid content concentration is more preferably 0.5 to 2% by weight, and most preferably 0.5 to 1.8% by weight. Outside of this range, it is extremely difficult to make the thickness of the obtained low refractive index layer to have a thickness necessary for sufficient reflection characteristics.

The thickness of the film substrate is not particularly limited, and is preferably 200 μm or less. When the thickness is thicker than 200 μm, the rigidity is too strong, and the obtained antireflection film is difficult to handle when it is adhered to the display.

The coating liquid used in the present invention is more preferably further contained in an alkoxy compound represented by the following formula.

(R ¹ O) _n MR ² _{m - n} wherein R ¹ and R ² are mutually independent alkyl groups having 1 to 4 carbon atoms, M is Al, Si, Ti or Zr, and m is an atomic valence equal to M The number, n is the number of 2 ~ m.

Such an alkoxy compound has a function of fixing the coated fine particles in the low refractive index layer.

Among the compounds represented by the above formula, hydrolyzable substances are preferred, and specific examples are methyltriethoxydecane, dimethyldimethoxydecane, trimethylacetoxydecane, tetraethoxycarbonyl. Decane, tetramethoxy decane, tetraethoxy decane, tetraisopropoxy decane, tetraisobutoxy decane, methyl triethoxy decane, dimethyl diethoxy decane, trimethyl ethoxy Alkane, phenyltriethoxydecane, etc. are suitable. Further, a catalyst may be contained in order to effectively carry out hydrolysis and condensation of the binder resin forming the low refractive index layer and the organic polymer covering the surface of the coated fine particles. The catalyst may use an acidic catalyst or a basic catalyst. The acidic catalyst is preferably an inorganic acid such as hydrochloric acid or nitric acid, an organic acid such as acetic acid, citric acid, propionic acid, oxalic acid or p-benzenesulfonic acid. The basic catalyst is preferably an organic metal compound such as ammonia, triethylamine or tripropylamine, an alkali metal compound such as sodium methoxide, potassium methoxide, potassium ethoxide, sodium hydroxide or potassium hydroxide.

The aging time of the coating liquid necessary for sufficient hydrolysis depends on the pH of the coating liquid, the ambient temperature and humidity, and is preferably aged for more than one hour.

The coating liquid in the present invention may further contain a crosslinking agent of the binder resin (b). The crosslinking agent crosslinks and hardens the binder resin when the coating film is dried.

Such a crosslinking agent may be a polyfunctional isocyanate compound, a melamine compound, an amine-based plastic resin or the like, and a polyfunctional isocyanate-based compound is more suitable from the viewpoint of ease of handling. Such polyfunctional isocyanate-based compounds are, for example, toluene diisocyanate, benzodimethyl diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate dimer, a terpolymer of a trimeric isocyanate or the like. Further, a blocked polyfunctional isocyanate compound blocked with a blocking agent such as a compound obtained by reacting such a polyfunctional isocyanate with a polyvalent alcohol, which contains two or more isocyanate groups, an anthraquinone or an indoleamine, and the like may be used.

The low refractive index film of the present invention can be provided by being applied on a uniaxially stretched laminated film. The coating method can be carried out by a method which is well known in the art. For example, lip direct method, small dot coating method, slit reverse coating method, die coating method, gravure coating method, blade coating method, spray coating method, pneumatic blade coating method, dip coating Method, rod coating method, etc. When a thermosetting resin is used as the binder, the coating of the low refractive compound is applied to the substrate by coating liquid containing the respective components, and dried by heating to form a coating film. The heating condition is 10 to 120 seconds at 80 to 160 ° C, and 20 to 60 seconds at 100 to 150 ° C is more suitable. When a UV curable resin or an EB curable resin is used as the binder, ultraviolet irradiation or electron beam irradiation is generally performed after preliminary drying.

[Examples]

The invention is illustrated in more detail by way of examples. Further, the physical properties and characteristics in the examples were measured or evaluated by the following methods.

(1) The melting point of the polyester resin and the glass transition point (Tg) were 10 mg of a polyester resin sample, and the melting point was measured at a temperature elevation rate of 20 ° C /min using DSC (trade name: DSC 2920, manufactured by TA Instruments Co., Ltd.).

(2) Thickness of each layer The sample was cut into a triangle shape and fixed in an epoxy resin embedded in a capsule. Then, the sample to be stored was cut into a film slice having a thickness of 50 nm in a film forming direction and a thickness direction by a sheet cutting machine (Uludo Lacado-S, manufactured by Lelyrudo Co., Ltd.). The obtained film sections were observed and photographed at an acceleration voltage of 100 kV using a transmission electron microscope (manufactured by JEOL Ltd., trade name: JEM2010), and the thickness of each layer was measured by photography. The layer thicknesses shown in Table 1 are defined as the layer thickness ratios shown below: the average thickness of the layer in the range of 0.05 to 0.5 in the first layer (3) The melting point of the film is determined by DSC, and the crystallization peak is taken as 10 mg. The sample film was subjected to DSC (manufactured by TA Instruments, trade name: DSC2920), and the crystallization temperature and melting point were measured at a temperature increase rate of 20 ° C /min.

(4) Reflectance and reflection wavelength A spectrophotometer (MPC-3100, manufactured by Shimadzu Corporation) was used, and a polarizing filter was attached to the light source side, and the wavelength of 400 to 800 nm was measured at each wavelength and the aluminum vapor-deposited mirror surface. Relative specular reflectivity. In this case, the measured value when the transmission axis of the polarizing filter is aligned with the stretching direction of the film is P-polarized, and the measured value when the transmission axis of the polarizing filter is orthogonal to the stretching direction of the film is made. For S polarized light. The average value of the reflectance of the respective polarizing components in the range of 400 to 800 nm is the average reflectance, and the maximum of the measured reflectances is the maximum reflectance, and the smallest is the minimum reflectance. The maximum reflectance difference in Table 3 is expressed by the following formula.

Maximum reflectance (%) = maximum reflectance (%) - minimum reflectance (%) (5) thickness of low refractive index film and refractive index film thickness and refractive index of low refractive index film by reflection spectroscopic film thickness meter (Manufactured by Otsuka Electronics Co., Ltd., trade name: FE-3000), the reflectance of 300-800 nm is measured, and the dispersion formula of n-k Koch is used as an approximation of the wavelength dispersion representing the refractive index, by the measured value of the spectrum The film thickness and the refractive index were fixed.

(5) Breaking strength The breaking strength in the film forming direction was obtained by cutting the sample film into a sample width (width direction 010 mm, length (film forming direction) 150 mm, 100 mm between chucks, stretching speed 100 mm/min, chart speed 500 m/min). Under the conditions, the sample was stretched using an Instron type universal tensile test apparatus, and then the breaking strength was measured from the obtained load-extension curve.

In addition, the breaking strength in the width direction was measured in the same manner as in the measurement of the breaking strength in the film forming direction except that the sample film was cut into a sample width (film forming direction) of 10 mm and a length (width direction) of 150 mm.

(7) The heat shrinkage rate of the heat shrinkage rate at 150 ° C for 30 minutes was maintained in an oven at a temperature set at 150 ° C for 30 minutes without stretching, and the dimensional change before and after the heat treatment was taken as heat shrinkage. The rate is calculated by the following formula.

Heat shrinkage rate %=[(L0-L)/L0]×100 L0: distance between marks L before heat treatment: distance between marks after heat treatment, and heat shrinkage rate at 10 °C for 10 minutes, at temperature setting The film was held in an oven at 200 ° C for 10 minutes without stretching, and the dimensional change before and after the heat treatment was taken as the heat shrinkage rate, and was calculated by the above formula.

(8) The thickness variation rate is cut into film samples having a film forming direction and a width direction of 1 m × 1 m, respectively, and then sheared into 25 pieces each having a width of 2 cm in the longitudinal direction and the lateral direction, using an electronic micrometer and a recorder. (K-312A, K-310B, manufactured by Anritsu Electric Co., Ltd.) The thickness of each sample was continuously measured. The average thickness was calculated from the total measured value, and the measured value was further subdivided into 200 mm, and the maximum value and the minimum value were read, and the thickness variation rate with respect to the average thickness was calculated by the following formula.

The rate of change of thickness (%) = (T _{m a x -} T _{m i n} ) / T _{a v e} where, T _{m a x} in the above formula is the maximum value of thickness, and T _{m i n} is the minimum thickness And T _{a v e} is the average thickness.

(9) Adhesive between layers The adhesive tape of 24 mm width (manufactured by Nichib Co., Ltd., trade name: 榭洛铁布) was adhered to a sample film (10 mm × 50 mm), and peeled off at a peel angle of 180 degrees. Stripping the surface. Each of the 10 samples was tested to calculate the number of times the interlayer peeling occurred.

(10) Differences in Hue For the standard light source C, L ^* , a ^* , and b ^* are obtained from the L ^* a ^* b ^* color system based on the JISZ8729 penetration spectrum of the sample film. The ab chromaticity product (c ^* ab) was obtained by the following formula, and the difference from the chroma of achromatic color was evaluated.

C ^* ab = {(a ^* ) ² + (b ^* ) ² } ^{1 / 2} ○: C ^* ab is less than 5 and is extremely excellent Δ: C ^* ab is 5 or more and 10 or less, and is practical ×: C ^* ab is 10 or more, it is not practical. (11) Enhancing the brightness effect The sample film is inserted between the polarizing plate and the diffusion film in the LCD panel (CMV CT-529A, manufactured by Chi Mei Co., Ltd.), and separated by a brightness meter (BM7) manufactured by Doppler. The front side brightness at the time of white was expressed by PC at 500 mm, and the brightness increase rate after the sample film insertion before the sample film insertion was calculated, and the effect of improving the brightness was evaluated.

◎: The brightness increase rate is 150% or more ○: The brightness increase rate is 140% or more and 150% or less ×: The brightness increase rate is less than 140% (12) The surface reflectance is UV-3101PC type manufactured by Shimadzu Corporation. An absorbing type polarizing filter is disposed on the light source side, and a black paint is applied to the antireflection layer side where the antireflection film is not formed, and light is irradiated on the side where the antireflection layer is formed, and the reflectance of the P polarized light and the S polarized light in the range of 300 to 800 nm is measured. The average value of the reflectance of 500 to 600 nm with high visibility is used as the surface reflectance.

[Example 1]

In the polyethylene (2,6-naphthalenedicarboxylate) (PEN) having an intrinsic viscosity (o-chlorophenol, 35 ° C) of 0.62, true spherical cerium oxide particles (diameter: 0.3 μm, long) Ratio of diameter to short diameter: 1.02, average deviation of particle size: 0.1) 0.15 wt% as polyester for first layer; preparation of intrinsic viscosity (o-chlorophenol, 35 ° C) 0.62 of terephthalic acid 10 mol The % copolymerized polyethylene 2,6-naphthalene dicarboxylate (TA10PEN) is used as the second layer polyester. Then, the first layer polyester and the second layer polyester were respectively dried at 170 ° C for 5 hours, and then supplied to an extruder, heated to 300 ° C to be in a molten state, and the first layer was divided into 301 layers by polyester. After the second layer is divided into 300 layers by polyester, the first layer and the second layer are alternately laminated, and the layer thickness is controlled by a multi-layer feeding unit continuously changing at a maximum/minimum of 3 times to maintain the lamination state directly. Introducing a die, and casting the thickness of each layer of the first layer and the second layer on the casting drum to 1.0:2.0 for casting, that is, making the first layer and the second layer alternately laminating a total of 601 layers of unstretched lamination film. The unstretched laminated film was stretched 5.2 times in the width direction at a temperature of 135 ° C, and heat-fixed at 245 ° C for 3 seconds. The thickness of the obtained uniaxially stretched laminated film was 55 μm.

A commercially available low-refractive-index forming coating material containing hollow cerium oxide fine particles retouched with a fluorinated organic compound, and a decane coupling agent and an acrylic resin as a main component (manufactured by Nippon Co., Ltd., trade name PX2-LR7) 5 g of the mixture was mixed with MIBK 66.2 g and 0.12 g of an isocyanate-based curing agent for 10 minutes to prepare a coating liquid. This coating liquid was applied on a single surface of a uniaxially stretched laminated film with a Meyer rod, and dried at a temperature of 150 °C. The hardening reaction was carried out for 1 minute to obtain a low refractive index layer. The film thickness was adjusted to 110 nm in the order of Meyer rods. The physical properties of the obtained uniaxially stretched multilayer laminated film are shown in Tables 3 and 4.

The reflectance of the low refractive index layer of this uniaxially stretched multilayer laminated film was 1.24.

[Embodiment 2]

The uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the double-sided coating was applied. The physical properties of the obtained uniaxially stretched multilayer laminated film are shown in Tables 3 and 4. The reflectance of the low refractive index layer of this uniaxially stretched multilayer laminated film was 1.24.

[Comparative Example 1]

The uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the double-sided coating was not applied. The physical properties of the obtained uniaxially stretched multilayer laminated film are shown in Tables 3 and 4.

[Example 3]

On the single side of the uniaxially stretched laminated film obtained in Comparative Example 1, a tetramer of tetrabutyl titanate (manufactured by Nippon Soda Co., Ltd., trade name: TBT B) was obtained by a micro gravure coating method. -4) Addition of 0.5% by weight of SiO ₂ fine particles of alkoxy metal to a petroleum-in/n-butanol (3/1) solution (manufactured by Yayalujiru Co., Ltd., Japan, R972, average particle diameter: 20 nm) Adding an additive dispersion of γ-glycidoxypropyltrimethoxydecane having a 15% by mole of a metal alkoxide; drying at 150 ° C for 2 minutes to form a film having a thickness of about 80 nm (refractive index) 1.75). Further, a 65 nm SnO ₂ layer (refractive index of 2.05) was formed by sputtering. Finally, tetraethyl phthalate was dissolved in ethanol, and SiO ₂ sol obtained by hydrolysis of water and hydrochloric acid was applied, and heat-treated at 100 ° C for 2 minutes to form a gel film (refractive index of 1.45), that is, uniaxially stretched multilayer Laminated film. The physical properties of the obtained film are shown in Table 3.

Fig. 1 is a graph showing an example of a reflectance of a wavelength of a polarizing component of light in a uniaxially stretched multilayer laminated film of the present invention.

Claims (6)

A uniaxially stretched multilayer laminated film characterized by (A) a first layer of a first thermoplastic resin having a positive stress optical coefficient and having a thickness of 0.05 to 0.5 μm, and a phase of the first thermoplastic resin The second thermoplastic resin obtained by the second thermoplastic resin is formed by a DSC-measured crystallization peak in the range of 150 to 220 ° C and a thickness of 0.05 to 0.5 μm in the second layer, and 501 layers or more are alternately present in a uniaxially stretched laminate. a film having a low reflectance layer having a reflectance of 3% or less on the incident side of the uniaxially stretched laminated film; wherein the first thermoplastic resin is in a completely repeating unit 95% or more of the amount of ethylene containing 2,6-naphthalene dicarboxylate (ethylene-2,6-naphthalene dicarboxylate) and having a melting point of 260 to 270 ° C, and the second thermoplastic resin is relative to The total repeat unit is from 75 to 97 mol% of ethylene glycol 2,6-naphthalenedicarboxylate and 25 to 3 mol% of ethylene terephthalate and/or isophthalic acid. Ethylene isophthalate unit and melting point of 210-255 ° C and higher than the above first thermoplastic resin The polyester having a melting point lower than 15 to 60 ° C, (B) the average reflectance of the parallel polarizing component for the surface containing the uniaxially stretched laminated film and the direction perpendicular to the direction of the film surface The range of the wavelength range of 400 to 800 nm is 90% or more, and the average reflectance of the vertical polarization component is 10 in the range of 400 to 800 nm in the direction of the film-containing stretching direction and the direction perpendicular to the film surface. %the following; Then, the (C) thickness variation rate is less than 5% and can be used for the reflective polarizing plate. The uniaxially stretched multi-layer laminated film according to the first aspect of the patent application, wherein the maximum reflectance of the parallel polarizing component in the range of wavelengths of 400 to 800 nm is applied to the surface containing the stretching direction of the film and perpendicular to the film surface. The difference from the minimum reflectance is 10% or less. The uniaxially stretched multilayer laminated film according to claim 1 or 2, wherein the vertical polarizing component is in the range of the wavelength range of 400 to 800 nm for the surface containing the stretching direction of the film and perpendicular to the film surface. The difference between the reflectance and the minimum reflectance is 10% or less. A brightness enhancement film for liquid crystal display, which is characterized by being formed by a uniaxially stretched multilayer film as disclosed in claim 1 of the patent application. A uniaxially stretched multilayer laminated film characterized by (A) a first layer formed of a first thermoplastic resin having a positive stress optical coefficient and having a thickness of 0.05 to 0.5 μm, and a first thermoplastic resin A uniaxially stretched layer in which a crystallization peak having a thickness of 0.05 to 220 ° C and a thickness of 0.05 to 0.5 μm is present in a second thermoplastic resin having a difference of 501 layers or more And a low refractive index layer having a refractive index of 1.1 to 1.45 on at least one side of the uniaxially stretched laminated film; wherein the first thermoplastic resin is contained in an amount of 95% by mole or more of the total repeating unit 2,6-naphthalenedicarboxylate having a melting point of 260-270 ° C, and the second thermoplastic resin being 75-97 mol % of 2,6-naphthalenedicarboxylate relative to the total repeating unit Acid glycol ester with 25~3 mol% of para-benzene Ethylene glycol dicarboxylate and/or ethylene glycol isophthalate unit and having a melting point of 210-255 ° C and 15 to 60 ° C lower than the melting point of the first thermoplastic resin; (B) containing the single The axially stretched laminated film is oriented in a direction perpendicular to the direction of the film surface, and the average reflectance of the parallel polarizing components is 90% or more in the wavelength range of 400 to 800 nm, and is perpendicular to the stretching direction of the film. The average reflectance of the vertical polarizing component in the direction of the film surface is 10% or less in the wavelength range of 400 to 800 nm. Then, the (C) thickness variation rate is less than 5% and can be used for the reflective polarizing plate. A method for producing a uniaxially stretched multilayer laminated film, which is characterized in that: the first thermoplastic resin having a melting point of 260 to 270 ° C is 15 to 60 ° C lower than the melting point of the first thermoplastic resin and a first step of forming a sheet by alternately laminating 501 layers or more of a second thermoplastic resin having a melting point of 210 to 255 ° C, wherein the first thermoplastic resin contains 2,6-naphthalene in an amount of 95 mol% or more of the total repeating unit. a carboxylic acid glycol ester having a melting point of 260 to 270 ° C, and the second thermoplastic resin is from 75 to 97 mol % of ethylene glycol 2,6-naphthalenedicarboxylate relative to the total repeating unit. 25~3 mol% of ethylene terephthalate and/or ethylene isophthalate unit and melting point of 210-255 ° C and lower than the melting point of the first thermoplastic resin 15~60 °C; a second step of stretching the obtained sheet in any direction of the drawing direction or the width direction by 2 to 10 times; and the obtained stretched sheet is 10 ° C lower than the melting point of the second thermoplastic resin The third step of heat treatment is carried out at a temperature between the temperature and a temperature 15 ° C lower than the melting point of the first thermoplastic resin.